How water looks

2012-08-05

Ocean's Shoreline

Hey all,
So finally I finished with Shoreline implementation. I know my work should be over by now but I'm happy with new things i'm learning each day. :D. Basically I took a foam texture (programmers art like) and blended it on ocean mesh where ever ocean touches terrain.
This is done by first getting all the points( These points are in world space) where ocean touches terrain and then scale them down to store it in an array. Till now all steps are pre-computed on CPU. That array is now passed to shader program. Now in a vertex program, nearest distance between vexter position and array of foam points is computed and then that distance is passed to fragment program. In fragment program foam Colour is clamped depending on the distance.

Important note:-
I got pretty much everything working with ease except for first step i.e. Getting the foam point.
To get foam points first I got terrain from engine into the water plugin. Then iterated over each terrain cell's height map. Now the thing took me so long was that The coordnate system usually start from bottom left corner so are iteration over cells. But when you are performing texture(heightmap) lookups the coordnates start from top left corner. It took me 7 days to understand this.

This is how it looks like:-

Side notes:-
*Array size is limited to 1000 a better way would be to create a texture and store all those points in it and perform a texture lookup in shaders
*This shoreline only works for Terrains. In order for them to work for any mesh, a plan collider can be used to get foam points. Rest of the steps would remain the same.

2012-06-30

Ocean Shaders

Ocean looked nice with connected meshes but it lacked reflection and refraction. Although Ocean is actually a deep water system thus should have no refraction but I did it anyways. For this implementation i followed this Paper.

It involved 5 basic steps.
1. Create the reflection texture : provided by engine
2. Create the refraction texture : provided by engine
3. Distort the textures according to a dudv-map :- We don't need it as it's used to apply distortion. Normal map worked equally great.
4. Apply bump mapping : not needed since we are using vertex shaders to generate waves.
5. Combine with fresnel effects : no problem :)

and here's the result

Ocean reflect refract

and this

island ocean

Some notes
-ocean exhibits No caustics. Caustics are already implemented in CS but aren't in ocean
-This shader is *not* shaderwaver. It is regular vertex and fragment program.
-LOD pops out as you move along.
-ocean doesn't entirely covers the island. a possible solution for it could be to increase the cell width and leght and corresponding parameters. so that it covers more area.
-also waves direction appears to be changing between different LOD when viewed from top. implementing inverse FFT could remove it, I think.

Modification in ocean LOD and mesh

So Crystal Space had a Ocean system in which Ocean was made by combining little ocean cells(20x20). These ocean cells would have different Level of Details(LOD) Governed by distance from camera. This distribution of LOD wasn't quite working as distance computed between camera and the cell was actually a *squared* distance and comparison was made with actual distance. Also cells re-positions themselves as camera move parallel to ocean. This re-positioning was causing a jerk. Well, both these bugs are fixed now. :)

Now comes the major issue *aaahhhh*. LOD distribution was working fine but the problem was with adjoining ocean cells of different LOD. for example one cell has LOD 5 and adjoining cell had LOD 4. Now LOD5 has double the vertices at boundaries than LOD4. and since the vertices are moving in waves like patterns so the ocean cells looks unconnected and Thus looked Ugly.

Thanks to Nvidia's ocean demo(and of course my mentor res) I was successfully able to replicate their implementation to rectify this problem. Checkout the wireframe rendering of ocean.
Here's what's happening.

Unmarked Oceancells

confused?
Now have a look at this

MarkedOceancell

Yellow color represents an oceancell.
Blue color represents inner mesh.
Green color represents the division line of outer meshes for a single cell.
there are four outer meshes for each cell.

The vertices for a cells are computed as usual. The real magic happens in computing the triangle(tris). tris for inner meshes are computed as usual. then 2^4=16 different cells are created for one LOD level and stored in an array.
2^4 where 2 is the resolution ie low/high and 4 are edges Top/right/bottom/left. That's how we got the number 16. Desired cell(out of 16) selection depends upon LOD level adjoining cell.